It is known to drive accessory devices for a vehicle, such as an alternator, water pump, or oil pump, using belts and pulleys driven by the crankshaft of the engine for the vehicle. Thus, the rotational speeds for the accessory devices have fixed ratios with respect to the rotational speed of the crankshaft. The accessory devices are normally sized to deliver full output at engine idle speed in order to allow full functionality at idle speed. As a result, during normal operation of the vehicle, when the crankshaft is rotating at speeds greater than the idle speed rotation, the accessory devices are being rotated much faster than required. Further, when the engine is turned off, the accessories come to a stop, which creates problems for stop-start and hybrid capable vehicles.